Electric trim in a QB kit

[mswain]

Thanks for the info. I am just now starting to build my tail and have been thinking a lot about all the various trim options. Something about having both manual AND electric trim appeals to me. most of the certified planes I have flown in the past had both, ie. when you hit the trim switch the trim wheel moves. Just trying to figure out how it's done, especially if there is an off the shelf option that will work.

[Mark Goldberg]

As I have said in the past - take BIG precautions that you do not get a runaway electric trim on a 4 place Bearhawk. If that happened it could be very bad. The trim is very powerful. Mark

[Battson]

The trim is powerful. We had a second - and even more realistic - runaway trim 'test' last August. I was caught totally unawares and off-guard, nonetheless the flight continued safely. Here's what happened:

A passenger rested their hand on the joystick trim button, and I didn't notice because I was map-reading at the time. It caused the trim to move to the upper limit (nose up). It gave me a quite fright as the aircraft pushed the stick into my hand and pitched rapidly upward. I wasn't expecting it. As with previous tests, returning the aircraft to straight and level flight was not difficult despite the trim being at limits and high stick forces. Once we were back in level flight, I could easily hold the plane steady and resist the stick force. After a few more seconds of resisting, I realised what might have happened, confirmed my theory with the instruments (trim position sensor / readout) and returned the trim to it's neutral position. We had a few jokes about it and carried on.

What this taught me:

- Trim runaway is a fully controllable situation, even during high speed cruise. A reaffirmation of our previous findings during the planned flight testing regime.
- Installing a trim runaway protection switch (pilot activiated) would be frivolous. The trim reached its limits (in 6 seconds) before I could identify the problem and stop the trim movement.
- Take care with my passenger briefings. Passengers are not to touch anything without asking (although it was accidental).

I don't want anybody to be scared of electric trim, I believe it is operationally superior. But to support Mark's point, there is plenty a builder can do to prevent electrical shorts to earth, in the trim control system. It is desireable to make the electrical system as robust as possible.

[Mark Goldberg]

Hi Jonathan. You noticed and took corrective action promptly. But not everyone might be as quick to notice or their corrective action might be too tentative at first. My experience is not that of a runaway trim. But if you land a BH and forget to re-trim and take off with landing trim - it is a handful. I have done it twice. It is all I can do to push the stick forward. I do not disagree with you if you prefer electric trim. Builders just need to understand what can happen. Mark

[Battson]

I agree Mark - ultimately the safety of the flight comes down to the pilot, particularly during unusual conditions.
I was careful to say that trim runaway is controllable - but I did not want to say it's "safe".